The InP(100) Surface Phase Diagram: From the Gas Phase to the Electrochemical Environment

The versatile optoelectronic properties of the material class of III-V semiconductors enable the highest performance in photovoltaic and photoelectrochemical solar cells. While a high level of control and understanding with respect to different surface reconstructions of these compounds in gas-phase ambient has been reached, the situation in an electrochemical environment still poses challenges. Here, we therefore have undertaken a computational study of the InP(100) surface in the presence of hydrogen and chlorine, mimicking the contact with a hydrochloric acid-containing electrolyte, aiming at an understanding of ion adsorption and dominant surface reconstructions with respect to applied potential and electrolyte concentration. For this purpose, the most stable surface terminations for hydrogen and chlorine (co)adsorption from the gas phase as well as the corresponding phase diagrams have been determined with respect to the hydrogen and chlorine chemical potential. In this context, we also introduce a quantitative type of phase diagram to highlight the stability of surface phases with respect to competing structures. Finally, by making use of the computational hydrogen electrode approach, these results were then transferred to the potential domain. We find that hydrogen (chlorine) adsorption is dominating at more (less) cathodic potentials, while coadsorption is limited to small fractions of the phase space. This allows us to determine experimentally accessible phases for which no detrimental effects, such as the creation of in-gap surface states, are to be expected.